ANTIOXIDANT ACTIVITY, SOME NUTRITIONAL AND COLOUR

TI
SCIEN
R
NO
UM POLO
AR
UM
ACTA
ISSN 1644-0730 (print)
Acta Sci. Pol., Technol. Aliment. 10(3) 2011, 327-338
ISSN 1889-9594 (online)
ANTIOXIDANT ACTIVITY, SOME NUTRITIONAL
AND COLOUR PROPERTIES OF VACUUM DRIED
STRAWBERRY TREE (ARBUTUS UNEDO L.) FRUIT
H. Hülya Orak1, Türkan Aktas1, Hülya Yagar2, S. Selen Isbilir2,
Neslihan Ekinci3, Fusun H. Sahin1
1
Namık Kemal University in Tekirdağ, Turkey
Trakya University in Edirne, Turkey
3
Çanakkale (18th March) University, Turkey
2
Background. The strawberry tree (Arbutus unedo L.) fruit contains a higher amount of
nutrients and bioactive compounds than many other cultivated species, however, the edible use of this fruit is currently not widespread. In this study, the influences of vacuum
drying have been investigated in terms of changing of some nutritional characteristics, antioxidant properties, and colour.
Material and methods. Fruits were collected from Çanakkale province in Turkey and
next vacuum dried. Ethyl oleate and water blanching pre-treatments were applied to fruits
before drying. Ascorbic acid, reducing sugar, minerals, colour, total phenolic content,
DPPH radical scavenging activity, β-carotene bleaching activity and HMF formation were
determined.
Results. The EO pretreatment shortened the drying time more than WB and gives a higher β-carotene bleaching activity, lower HMF and higher yellowness and brightness of external colour characteristics.
Conclusions. In this research, the effects of vacuum drying process on the colour, antioxidant activity and nutritional characteristics of fruit have been determined and it has been
concluded that the strawberry tree fruit is assessable in food industry by drying due to rich
nutritional components, antioxidant activity and attractive colour of the fruit.
Key words: Arbutus unedo L., DPPH activity, ascorbic acid, minerals, colour, pretreatments, vacuum drying
© Copyright by Wydawnictwo Uniwersytetu Przyrodniczego w Poznaniu
Corresponding author – Adres do korespondencji: Ph.D. H. Hülya Orak, Department of Food
Technology of Vocational School of Technical Sciences of Namık Kemal University, 59030
Tekirdağ, Turkey, e-mail: [email protected]
328
H.H. Orak ...
INTRODUCTION
Arbutus unedo L., the strawberry tree (Ericaceae family) fruit, is an evergreen shrub
or small tree and it is widely distributed in the Mediterranean region and North Africa.
This fruit is suitable for the production of alcoholic beverages, jams, jellies and marmalades [Pallauf et al. 2008] and in some countries, such as Spain and Morocco, Arbutus
unedo is frequently used in the traditional medicine [Tahraoui et al. 2007].
Drying is one of the most widely used methods for fruit preservation. Sun drying is
the most common method, because it uses a natural resource/source of heat: sunlight
[Doymaz and Ismail 2010]. But sun drying is not possible as a drying method for this
fruit, because Arbutus unedo appears in clusters and ripens in the autumn and winter
months. Therefore, other drying techniques are needed for drying of Arbutus unedo
fruits and it is known that vacuum drying may allow to obtain high quality products
[Muthukumaran et al. 2008]. Generally, in fruits, drying is controlled by wax cuticle
in the fruit skin and the drying rate can be increased by means of removing the surface
of fruits and by chemical pre-treatments, such as ethyl oleate or potassium carbonate
[Doymaz 2007]. Ethyl oleate has been commercially used to accelerate the drying and it
is applied to the surface of the fruit by dipping, resulting in a coating which apparently
breaks down the waxy cuticular on fruit surface, and this way the resistance to moisture
loss is reduced in fruit skin [Williams 1989]. Blanching is also one of the most widely
used pre-treatment because of inactivation of enzymes, and it changes the tissue structure, which results in shortening the drying time and in increasing the drying rate
[Doymaz 2008].
The antioxidants are vital substances which possess the ability to protect the body
from possible harms caused by the free radical [Percival 1998]. Hence, there has been
an increasing interest in different medicinal and dietary plants and their antioxidant
potential. During the drying process, it is well known that numerous physical, chemical
and nutritional changes occur in the fruits, which can affect their quality attributes
[Di Scala and Crapiste 2008]. This research was performed to determine the changes
in antioxidant activity, as well as nutritional characteristics and colour properties of
vacuum dried strawberry tree (Arbutus unedo L.) fruit and the effects of applying ethyl
oleate and water blanching pretreatments.
MATERIAL AND METHODS
Material. Ripe fresh strawberry tree (Arbutus unedo L.) fruits were collected from
Turkey Çanakkale province, Lapseki subprovince and Şevketiye village at 100-200 m
above sea level.
Drying experiments. Strawberry tree fruits were treated by two different applications in order to increase the water permeability of berries. In first pretreatment, whole
berries were dipped into 2% ethyl oleate + 4% potassium carbonate solution [Doymaz
2008] for one minute at room temperature (Ethyl oleate application; EO). In second
pretreatment, whole berries were dipped in hot water (80°C) for one minute. The temperature was determined to be 80°C after various blanching pretreatments, because the
texture of berries remained tough at this temperature (Water blanching application;
WB). Control samples with non pre-treatment (NPT) were also prepared for compari-
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Antioxidant activity, some nutritional and colour properties of vacuum dried ...
329
son. Before the drying process, all berries were transversely divided into two halves.
Drying experiments of samples were carried out at the drying temperature of 65°C and
at the vacuum chamber pressure of 10 kPa by using the lab-scale vacuum dryer (MMM
Medcenter Vacucell 22 Blue Line Vacuum Dryer). A batch of 300 g sample was placed
on a tray and arranged in one single layer.
Drying processes for every treatment (NPT, EO and WB) were continued to reach
approximately the same moisture content (10% w.b.). The wet-basis moisture content
which is expressed as the ratio of moisture mass to the total mass of the substance, were
calculated during the drying experiments. The ratio is represented by the following
equation:
MC wb 
m water
 100
m water  m dm
In this equation MCwb is wet-basis moisture content in %, mwater is mass of moisture
in kg, and mdm is mass of dry matter in kg.
Preperation of sample extract. For ethanol extraction of dried fruits, 5 g of ground
samples were mixed with 250 mL of ethanol and the mixture was shaken by using Edmund Buhler-KS-15 shaker (at 180 rpm constant speed) for one night at room temperature. Ethanol solution was filtered through Whatman No. 4 filter and the residue was
reextracted twice and filtered. All extracts were pooled and solvents were removed by
using a rotary evaporator (IKA-Werke GmbH and Co. KG) under vacuum at 45°C.
To determine the fresh fruit antioxidant activity properties, lyophilised samples were
used for ethanol extraction. For lyophilisation, berries divided in 4 pieces were frozen
by blast and fluid bed freezer (Armfield; FT 36) at –40°C immediately, later crushed
and lyophilised by vacuum freeze drier (plate temperature at 10°C) and after then extracted by ethanol using the same procedure.
Total phenolic content (TPC). Total phenolic content in the extracts was determined
by Folin-Ciocalteu reagent of Slinkard and Singleton [1977] method using gallic acid
as a standard phenolic compound at a range between 50 and 500 g/mL (r2 = 0.9897).
The amount of total phenolic compounds was expressed as mg of gallic acid equivalent
(GAE).
DPPH radical scavenging activity. To determine the DPPH radical scavenging activity, the extracts were evaluated by 1,1-diphenyl-2-picryl-hydrazil (DPPH•) using the
Blois method [1958] by using a spectrophotometer (Shimadzu UV-1601) at 517 nm.
The antiradical activity was calculated using the ratio: (Acontrol – Asample / Acontrol) × 100,
where Acontrol is the absorption of the DPPH• solution and Asample is the absorption of the
DPPH• solution after the addition of the sample.
Total antioxidant assay using β-carotene bleaching method. Total antioxidant activity by using β-carotene bleaching method was carried out by the spectrophotometric
method of Miller [1971] based on the ability to decrease the oxidative bleaching of β-carotene in a β-carotene/linoleic acid emulsion and the absorbance of the mixtures was
read at 490 nm. Total antioxidant activity (TAA) was expressed as the percentage of
inhibition relative to the control after a 120 min incubation period [Al-Saikhan et al.
1995], as below: TAA = 100(DRC – DRS)/DRC, where: DRC – degradation rate of control = ln(a/b)/120, DRS – degradation rate of sample = ln(a/b)/120, a and b – absorbance
of samples and controls at 0 and 120 min.
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H.H. Orak ...
Other analysis methods. Dry matter content of Arbutus unedo berries was determined by using a vacuum dryer at 70°C [Cemeroglu 2007]. Ascorbic acid content (AA)
of samples was analysed according to the method described by Cemeroglu [2007],
which is by using 2,6-dichlorophenolindophenol solution as indicator and the absorbance was measured at 500 nm on a Hitachi 2000 UV/Vis spectrophotometer. The reducing sugar content of berries was assayed according to Ross [1959] by using 2,4-dinitrophenol reactive and glucose as a standard. The measurements were made at 600 nm by
a spectrophotometer (Hitachi UV/Vis –2000). The 5-hydroxymethylfurfural (HMF)
content was determined quantitatively following the procedure described by Cemeroglu
[2007], which is based on the colorimetric reaction between barbituric acid, p-toluidine
and HMF, forming a red colour complex. Mineral contents in samples were determined
by an inductively coupled plasma atomic emission spectrometer (ICP-AES) with a microwave burning unit (30 min at 200 PSI, 2008C, 1,200 W) [Skujins 1998]. The working conditions of ICP-AES (Varian-Vista) were the fallowing; RF power 1.5 kW for
axial, Plasma gas flow rate (Ar) 17 L/min (radial), Auxiliary gas flow rate (Ar) 0.2,
Viewing height 15 mm, Copy and reading time 5-10s (max. 60 s). Colour measurements
of the samples were performed by using Hunter-Lab tristimulus colorimeter (D25LT
model). CIE L*, a*, b* colour parameters and yellowness index (YI) of samples were
measured from 10 points of every sample pile just after drying processes. Colour parameters were measured either for exterior (skin) or inner fleshy part. In the CIE L*, a*, b*
colour system L* value represented the lightness of colour (0 – black, 100 – white),
a* represented the redness (positive values) or greenness (negative values) colour,
and b* represented the yellowness (positive values) and blueness (negative values)
colour [Hunter... 2006].
Statistical analysis. Statistical analysis was carried out by the method given by
Steel and Torrie [1960], which is by using the MSTAT packaged program.
RESULTS AND DISCUSSIONS
As shown in Figure 1, the drying time was shortened approximately for 3 hours
by using the ethyl oleate pretreatment. Water blanching also shortened the drying time,
but the effectiveness of this pretreatment was found to be lower than that of the ethyl
oleate application. In different drying studies, some chemical applications with ethyl
oleate gave better results for different materials. The short drying time of the vacuum
dried strawberry tree fruits using the EO pre-treatment can be explained by the fact that
this solution removes the waxy layer from the surface of berry and increases the skin
permeability similar to its effects on other fruits, such as strawberry, seedless grapes and
apricots [Doymaz 2008].
The reducing sugar content of fresh fruit increased approximately two times in dried
berries due to the moisture loss. On the other hand, in dry matter the reducing sugar
content of the pretreated berries show statistically significant (P < 0.05) loses. The results show that WB application caused higher sugar loses than those of EO pretreatments. This higher loss can be explained by the fact that a higher temperature of
water and an increase in the solubility may increase the reducing sugar content. The
lowest value of reducing sugar decreae was determined also in NPT samples, and from
these results can be concluded that the sugar content of dried berries was affected by
pretreatments rather than by drying (Table 1).
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0.80
NPT
Moisture content, % w.b.
0.70
EO
0.60
WB
0.50
0.40
0.30
0.20
0.10
0.00
0
5
10
15
20
25
30
Drying time, hour
Fig. 1. Decreasing of moisture content of strawberry tree
(Arbutus unedo L.) fruit in vacuum drying process
at 65°C
Retention of ascorbic acid
in dry matter of sample, %
Extract yield g/100 g of fruit
%
Total phenolic content
µg GAE/g extract
Total phenolic content
in dry matter, µg GAE/g
Reducing sugar
g/100 g
Reducing sugar in dry matter
g/100 g DM
Retention of reducing sugar
in dry matter of sample, %
HMF, mg/kg
nd
70.34
±1.42a
14.29
±0.71a
10.06
±0.68a
9.97
±0.53b
22.74
±0.63a
nd
nd
NPT
88.68 144.90 164.39
±1.11a ±2.33b ±1.72b
37.45
68.88
59.34
±1.84c
2.62
±0.42c
1.26
±0.52d
19.85
±0.09a
22.38
±0.60ab
1.58
2.49
±0.56a
EO
89.06 134.20 150.68
±1.51a ±3.04b ±0.76b
42.07
71.49
63.49
±1.23b
3.61
±0.41c
2.30
±0.44b
19.53
±0.09a
21.92
±0.65c
3.61
1.45
±0.86c
WB
90.03 124.40 138.18
±1.14a ±1.96c ±1.55c
46.30
73.85
57.09
±1.54d
4.53
±0.41b
2.35
±0.44b
18.78
±0.41a
20.86
±0.85d
8.26
2.25
±0.26b
1.075
0.532
0.047
1.797
0.511
LSD %5
2.093
6.002
Ascorbic acid in dry matter*
mg/100 g DM
nd
Ascorbic acid
mg/100 g
43.84 231.66 528.42
±1.07b ±3.52a ±2.29a
Dry matter content
g/100 g
Fresh
fruit
Analysed samples
Retention of ascorbic acid
in dried fruit, %
Table 1. Effect of pretreatments and vacuum drying process on dry matter, ascorbic acid, total
phenolic and reducing sugar content of strawberry tree (Arbutus unedo L.) fruit and
HMF formation
15.825
0.006
*To determine the effectiveness of drying method on fruits, analysed values were expressed in dry weight basis.
NPT – non pre-treated dried fruits, EO – ethyl oleate applied dried fruits, WB – water blanching applied dried fruits.
Different letters of upper index within the column indicate significant differences at P < 0.05 level (n = 3).
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332
Colour parameters of L*, a*, b* and YI for fruits were evaluated from external and
internal side in dried fruits, because the colour of fruit is red on external side and deep
yellow on internal side (Fig. 2 a and 2 b). Proliac and Raynaud [1981] reported that
carotenoids may be responsible for yellow colour in the flesh of the fruits, and that the
external red colour is mainly due to the presence of other phenolic pigments, identified
as 3-glucosylcyanidin. As seen in Figs 2 a and 2 b, the decrease on redness (a*) in internal side was not affected by drying and pretreatments, and differences were found to be
insignificant (P < 0.05). The decrease of the yellowness (b*) of internal side was found
significant and pre-treatments demonstrated effectiveness on saving the yellowness.
Therefore, it can be concluded that the decrease of carotenoids in fleshy part of fruit was
significantly affected by the drying process. Similarly, the drying process significantly
effected the decrease of the external red colour, but the effect of pretreatments was
found to be insignificant. On the external side, the yellowness (b*) also decreased significantly after drying process, but EO pre-treated samples were found to be of higher
yellowness than the NPT samples (Fig. 2 a). The brightness (L*) of the dried fruits also
decreased both on external and internal sides and they were differently affected by EO
and WB pretreatments. It is shown that the decrease in internal side brightness was
higher than in external side brightness. As seen in Figs 2 a and 2 b, the differences between the degrees of yellowness change, namely the yellowness index (YI) of both, the
skin side and the inside part of strawberry tree fruits, and after drying were found statistically insignificant. In terms of pretreatments, it can be seen that EO saved the brightness of external colour higher than WB. In general evaluation, the external colour of
fruits was found to be better in EO pretreatment in terms of brightness and yellowness.
Ergunes and Tarhan [2006] found that all the pretreatments using ethyl oleate significantly accelerated the drying process, but the using of only 2% ethyl oleate decreased
all colour parameters, while using the solution that contains 2% NaOH increased the all
colour parameters remarkable. The future research should examine the effects of EO
solution, including NaOH, on colour of fruit.
(a)
FRESH FRUIT
NPT
EO
(b)
WB
Hunter colour values
60
40
10
60
b
b
aaaa
bc c
cc
40
a
c
b
c
30
EO
WB
a
a
b b
b
50
a
30
20
NPT
70
a
50
FRESH FRUIT
b b
c
a
c d
a
b
c b bc
20
10
0
0
a internal a external b internal b external
Hunter colour parameters
L internal
L external YI internal YI external
Hunter colour parameters
Fig. 2. Hunter colour parameters (a*, b*, L and YI values) of fresh and dried strawberry tree
(Arbutus unedo L.) fruit. Values were determined both external and internal side of
fruit. Different letters of upper index within the column indicate significant differences at P < 0.05 level (n = 3): LSDai = 2.010, LSDae = 2.140, LSDbi = 2.975, LSDbe =
1.047, LSDLi = 0.947, LSDLe = 0.891, LSDYLİ = 8.023, LSDYLe = nd
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The degree of browning is the most common method for brown pigment detection
[Labuza and Baiser 1992], while the formation of 5-hydroxymethylfurfural (HMF) has
been widely used as an indicator. In Table 1 it is shown that EO pretreatment gave better
results than other applications. It could be a result of the berries being exposed to
a shorter heat time in EO application. It can be concluded that the EO pretreatment may
inhibit the formation of HMF during the drying
Ascorbic acid (AA) retention can be used as a quality index of dried products, because,
if ascorbic acid content is well retained, the other nutrients are also generally preserved
[Shitanda and Wanjala 2006]. The initial content of ascorbic acid in fresh berries decreased significantly (Table 1). There were no significant differences found in AA content
between NPT and EO pretreated berries. The WB application caused the higher degradation of AA, and AA los was found to be 46.30% in dried fruit. The berries dipped in solution in both pretreatments indicated that the loses can arise due to the higher temperature
of solution by WB pretreatments. According to our results, it can be said that AA retention
occurres significantly in fruits by drying process and pretreatments.
In the drying process, the protection of phenolic content is a very important issue
because of the known antioxidant activity of the phenolic compounds. After the drying
process, the total phenolic content of berries decreased significantly and the pretreated
samples exhibited a higher phenolic content than the NPT fruits. Although the phenolic
content was determined to be higher in WB treatment than in EO, there were no statistically significant differences in dry matter content (Table 1). In a previous study, Wen
et al. [2010] explained that blanching process had different effects on different vegetables, and while some vegetables showed increased phenolic content, others revealed
a decreasing phenolic content.
The antioxidant activity of fresh and dried berry ethanolic extracts were determined
according to the free radical-scavenging activity (DPPH) and β-carotene bleaching
assay methods. DPPH method is based on the reduction of DPPH in the presence of
a hydrogen-donating antioxidant due to the formation of the non-radical form DPPH
[Shon et al. 2003]. As it can be seen from Figure 3, the inhibition effects of extracts
Inhibition, %
FRESH FRUIT
100
90
80
70
60
50
40
30
20
10
0
NPT
EO
WB
a
a
c
a
c
c
c
250
c b
c b
b
500
1000
Extract concentration, µg/mL
Fig. 3. DPPH Radical-scavenging activity in the ethanolic extracts
of fresh and dried strawberry tree (Arbutus unedo L.) fruit.
Different letters of upper index within the column indicate
significant differences at P < 0.05 level: LSD250 = 0.725,
LSD500 = 0.886, LSD1000 = 0.99, n = 3
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334
increased with increasing concentration and the DPPH scavenging activity of fresh fruit
was determined to be 91.03 ±1.18% at 1000 µg/mL concentration. On the other hand,
the scavenging activity decreased significantly after the drying process, and it was
found to be 54.13 ±0.64% in NPT fruits. In terms of pretreatment, WB application resulted in a slightly higher scavenging activity, because of the including of higher phenolic contents of extracts. The EC50 value is the effective concentration which is required to decrease the initial DPPH• concentration by 50% and lower EC50 value reflects
better protective action. Lower EC50 value corresponds to the highest scavenging activity of DPPH radicals. The lowest EC50 values were found in fresh berry extracts as 1.841
mg/mL, and it was 5.992 mg/mL for WB, 6.627 mg/mL for EO and 7.814 mg/mL for
NPT.
The reduction in absorbance of β-carotene–linoleate emulsion in the presence of the
ethanol extracts of fresh and dried berries is shown in Figure 4. In the β-carotene-linoleate system, the inhibition effects of pre-treated fruits were determined to be lower than
those of fresh berries at all concentrations. The lowest inhibition effect of β-carotene
bleaching was determined in NPT extract. The pretreated fruits exhibited a higher activity than NPT, and EO pre-treatment was found that had higher affect on activity. This
case may be interest to apolar character of EO in the apolar reaction medium which
carried out β-carotene bleaching assay. If antioxidant activity was expressed according
to β-carotene bleaching system, EO pre-treated fruits were found to have a higher activity. It may explain why lower drying time causes the lower degradation of active phytochemicals.
FRESH FRUIT
NPT
EO
80
a
Inhibition, %
70
60
a
a
b
50
40
30
WB
b
c
c
d
b
b
c
d
20
10
0
250
500
1000
Extract concentrations, µg/mL
Fig. 4. β-carotene bleaching activity of ethanolic extracts of fresh and
dried strawberry tree (Arbutus unedo L.) fruit. Different letters
of upper index within the column indicate significant differences at P < 0.05 level (n = 3): LSD250 = 9.372, LSD500 = 5.53,
LSD1000 = 7.380
The mineral contents of the fresh and vacuum dried berries are given in Figs 5 a and
5 b. As shown in these figures, Ca, K, and P are the predominant minerals in fresh and
dried samples. The mean values of these minerals in fresh berries were determined as
645.55 ±90.98 mg/kg FW, 2931.53 ±467.24 mg/kg FW and 492.92 ±69.69 mg/kg FW,
respectively. The mineral contents was expressed in dry matter in fresh and dried fruit
and exhibited in related figures to compare the drying method effects on mineral contents
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Antioxidant activity, some nutritional and colour properties of vacuum dried ...
(a)
FRESH FRUIT, mg/kg FW
EO, mg/kg DM
50
45
FRESH FRUIT, mg/kg DM
WB, mg/kg DM
a
a
40
NPT, mg/kg DM
a
b b
b
35
30
mg
335
b
25
18.09
a
c c
12.08
15
d
17.14
18.11
20
c
c
a b
c b
b
c c
10
6.8
5
0
Zn, mg/kg
Cu, mg/kg
B, mg/kg
S, mg/100 g
Fe, mg/kg
Minerals
(b)
FRESH FRUIT, mg/kg FW
FRESH FRUIT, mg/kg DM
EO, mg/kg DM
WB, mg/kg DM
1800
a
1600
b
1400
c
1200
mg
NPT, mg/kg DM
d
a
1000
800
645.55
293.15
400
c
d
a
a
b c c
600
b
240.73
b
c
492.72
d
200
0
Ca, mg/kg
K, mg/100 g
Mg, mg/kg
P, mg/kg
Minerals
Fig. 5. Mineral matter content of fresh and dried strawberry tree (Arbutus unedo L.) fruits.
Amount of mineral content values for fresh fruit were given in both column. First column shows amount of mineral content in fresh weight of kg (mg/kg FW) while second column shows amount of mineral content in dry matter of kg (mg/kg DM) fruit.
Different letters of upper index within the column indicate significant differences
at P < 0.05 level (n = 3): ZnLSD = 1.968, CuLSDa = 0.405, FeLSD = 0.701, CaLSD =
2.250, KLSD = 10.069, MgLSD = 4.984, PLSD = 2.310, SLSD = 5.484, BLSD = 1.796
(Figs 5 a and 5 b). As it can be seen from these figures, the Fe, Ca, K and P contents
in the dried berries are approximately twice higher than in the fresh samples wet weight
due to the increasing of the dry matter content, and these results confirm Arslan and
Ozcan [2010]. The reduction in mineral content by drying were determined to be important statistically (P < 0.05). Zn and Cu showed a more considerable decrease than
other minerals in drying fruit with respect to the fresh samples. Addditionaly, Cu, K,
Mg, P, S and B contents of dried berries were found to be lower in WB pre-treated samples than in the EO. WB pre-treatment increases the losses of these minerals. In EO
Acta Scientiarum Polonorum, Technologia Alimentaria 10(3) 2011
336
H.H. Orak ...
application, although the berries were dipped in solution, the WB process may increase
the amount of mineral losses, because of the higher temperature of water in the WB pretreatment which could cause an increase in the solubility of the elements more than the
EO pre-treatment. In general, it can be concluded that the water blanching process further increased the loss of minerals, except Ca. The Ca value was found to be lower in
EO pre-treated samples and this decrease may be a result of resolution of the Ca when
solving the waxy substances from external surface at the same time. The level of K was
high in all samples, which can be considered to be an important indicator due to the fact
that many enzymes use them as cofactors [Ozcan and Haciseferogullari 2007].
CONCLUSIONS
In conclusion, the vacuum drying process shows significant effects on the colour,
antioxidant activity and nutritional characteristics of strawberry tree fruit. In dried fruits,
the reducing sugar content and the minerals content were found to be higher than in
fresh berries, because of the increased dry matter content. EO pre-treatments shortened
the drying time and some fruit characteristics were affected positively by using this
pretreatment. Therefore, the strawberry tree fruit is usable in food industry with its
preservation by drying method and due to the rich nutritional composition, antioxidant
activity and attractive colour. The future studies should focus on a better protection of
the antioxidant potential and nutritional composition of fruit by using different drying
methods and pretreatments.
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WŁAŚCIWOŚCI ANTYUTLENIAJĄCE, BARWA I WŁAŚCIWOŚCI
ŻYWIENIOWE LIOFILIZOWANYCH OWOCÓW CHRÓŚCINY JAGODNEJ
(ARBUTUS UNEDO L.)
Wstęp. Chociaż owoce chróściny jagodnej zawierają więcej substancji odżywczych oraz
substancji bioaktywnych niż wiele innych owoców, obecnie nie jest powszechne ich spożycie. W przedstawionej pracy badano wpływ bioliofilizacji na zmiany w wartości żywieniowej, barwie oraz zawartości substancji bioaktywnych zawartych w tych owocach.
Materiał i metody. Owoce były zbierane w Turcji w prowincji Çanakkale. Po wstępnej
obróbce (blanszowanie oraz dodatek oleinianu etylu) były poddane liofilizacji. Oznaczono
zawartość: kwasu askorbinowego, cukrów redukujących, soli mineralnych, związków fenolowych, aktywność DPPH, powstawanie HMF oraz zmiany barwy.
Wyniki. Wstępne działanie EO skracało czas suszenia bardziej niż WB i wpływało na zachowanie większej wartości aktywności ß-karotenowej, mniejszej wartości HMF oraz
większych wartości jasności i tonu żółtego w barwie wyrobu.
Wnioski. W pracy zbadano wpływ liofilizacji na barwę, właściwości antyutleniające oraz
właściwości żywieniowe badanych owoców. Ustalono, że owoce chróściny jagodnej mogą być wykorzystane w przetwórstwie spożywczym ze względu na ich dużą wartość żywieniową, właściwości utleniające oraz atrakcyjną barwę.
Acta Scientiarum Polonorum, Technologia Alimentaria 10(3) 2011
338
H.H. Orak ...
Słowa kluczowe: Arbutus undeo L., chróścina jagodna, liofilizacja, DPPH, kwas askorbinowy, sole mineralne, barwa, obróbka wstępna
Received – Przyjęto: 15.02.2011
Accepted for print – Zaakceptowano do druku: 27.03.2011
For citation – Do cytowania: Orak H.H., Aktas T., Yagar H., Isbilir S.S., Ekinci N., Sahin F.H.,
2011. Antioxidant activity, some nutritional and colour properties of vacuum dried strawberry
tree (Arbutus unedo L.) fruit. Acta Sci. Pol., Technol. Aliment. 10(3), 327-338.
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